1. Field of the Invention
This invention relates generally to photoconductive films having an insulated conductive layer for use with a microfilm camera, and particularly to a spring clip utilized to ground the conductive layer to the camera.
2. Description of the Prior Art
Microfilm cameras exist which may be used to transfer a greatly reduced image of an object document to a strip or card for storage and subsequent retrieval. These cameras utilize an intermediate photoconductive film for the development and subsequent transfer of the image to the strip or card. As shown in FIG. 1, the film 10 is a laminated structure which includes a polymer protective sheet 12, a thin conductive layer 14, a photoconductive layer 16 and a silicone release layer 18. The polymer sheet 12 is an insulating layer which contributes to the structural strength of the film 10 and protects the conductive layer 14, which is typically vapor-coated aluminum. The photoconductive layer 16 can be either an organic photoconductor or a dispersion of an inorganic photoconductor in particulate form dispersed in a suitable binder. The silicone release layer 18 is one of a class of film-forming silicone polymers which are described in U.S. application Ser. No. 520,208, filed by Hendrickson on Aug. 4, 1983.
The photoconductive film 10 is used within the camera in an electrographic process which involves placing a uniform electrostatic charge on the photoconductive layer 16, exposing the layer to light to dissipate the charge in areas of the layer 16 exposed to light and developing the resulting electrostatic latent image by depositing on the image area a finely divided electroscopic material commonly referred to as toner. The toner will be attracted to those areas of the photoconductive layer 16 which retain a charge, thereby forming a toned image corresponding to the electrostatic latent image. The toned image may then be transferred to a receptor surface such as a strip or card of paper or polymeric film. The conductive layer 14 is necessary to conduct the electrical charge away from the exposed areas to a suitable ground, and the silicone release layer 18 facilitates the transfer of the toner image to the receptor surface.
In order that the conductive layer 14 may effectively conduct the charge away from exposed areas, the conductive layer 14 must be grounded to the microfilm camera in which the photoconductive film 10 is used. Direct access to the conductive layer 14, however, is prevented by the polymer sheet 12 which supports and protects the conductive layer 14 and the photoconductive layer 16. In the past, it has been a practice to dissolve a portion of the photoconductive layer 16 at an end of the film 10 with a solvent in order to gain access to the conductive layer 14. This procedure is time consuming and inconvenient.
A similar problem of access to a conductor through a thin insulating film was addressed in U.S. Pat. No. 3,818,415 in which an electrical terminal was provided which included abrasive particles bonded to the surface of the terminal. An electrical connection to the film insulated conductor was obtained by sliding the conductor over the terminal surface while the two parts were held together. The abrasive particles on the terminal scored the insulating film and thereby exposed the metallic conductor. While effective, this manner of producing an electrical connection to the conductive layer 14 may result in abrasive particles being scraped from the terminal surface and interferring with the workings of the associated apparatus.